1. Field of the Invention
The present invention generally relates to electrical couplers and, more particularly, is concerned with an improved male electrical plug assembly with increased electrical creepage distance between contacts.
2. Description of the Prior Art
Locking electrical couplers having male plugs and female connectors which first mate and then rotate relative to one another have been commercially available for many years for application in numerous industrial and special uses. These electrical couplers have generally incorporated 3 to 5 electrical contacts and have been rated at 20, 30, 50 and 60 Amps and from 125 VAC to 250 VAC and to 600 VAC.
Traditionally, the interior current-carrying portion of the male plugs of these electrical couplers were manufactured by insert molding of forged or sintered electrical contacts, having swaged or wrought terminal shanks, into a thermoset insulating body. This traditional construction has both important advantages and disadvantages. The advantages are that the integrally molded assembly is resistant to both axial and rotational forces on the electrical contacts and that electrical creepage distances are limited only by the established configuration. Creepage distance refers to the shortest distance along the surface of insulating material between two conductive parts.
The disadvantages are that the thermoset molding cycle is extremely slow and the molds are susceptible to damage due to misplaced contact inserts. Also, insert molding requires the assistance of an operator. Further, post-molding machining is necessary to remove over-molded insulating material from the working surfaces of the contacts and to assure the tolerances required by the configuration for the diameters of these working surfaces. Furthermore, the thermosetting materials available have limited impact strength. The molding cycle time and the impact strength could be addressed by insert molding with a thermoplastic material, but the cost of the molds at risk from misplaced inserts would be much greater and the configuration would require section thicknesses which could not be molded in thermoplastic without excessive shrinking, sinking, voids and dimensional discrepancies.
Attempts have been made to replace the traditional insert molded/thermoset construction with an alternative constructional approach involving post molding assembly of electrical contacts and thermoplastic insulating parts. However, this alternative approach does not retain the inherent resistance of the traditional construction to axial forces on the contacts. Instead, the alternative approach relies on a small threaded fastener to resist separation due to tensile forces. Also, the minimum electrical creepage distance provided under the alternative approach is not commensurate with the 600 VAC rating of the electrical coupling device. The measured electrical creepage distance of one commercial device employing this alternative approach is only approximately 5.5 mm, whereas established international standards provide for electrical creepage distances ranging from 8 to 10 mm, depending upon the respective materials used.
Consequently, a need still exists for improvement in the construction of the male plugs for locking electrical couplers. The type of improvement desired is one which will retain the advantages of the traditional construction approach for male plugs while eliminating the disadvantages thereof but without introducing new disadvantages in the place of the old ones being eliminated.